Temperature gradient bar sealer

ABSTRACT

Apparatus for and a process of heat-sealing various materials such as plastics, papers, laminates and coatings. The apparatus can be used for several purposes such as determining the optimum temperature at which a given heat-sealing operation should be conducted under given conditions of pressure and dwell time and to effect increased quality control by maintaining the temperature at which the heat is supplied during the heat-sealing operation under given conditions of pressure and dwell time.

United States Patent [72] Inventor Howard A. Rohdln 2,701,926 2/1955Meyer Wlquoit, Mass. 3,393,292 7/1968 Ritscher 219/245 [21] Appl. No.815,477 2,844,956 7/1958 Smith 73/150 X [22] Filed Apr. 11,19692,958,366 1/1960 Conti 156/378 [45] Patented Nov. 30, 1971 3,148,2699/1964 Van Hartesve1dt et a1. 219/243 [73] Assignee PackagingIndustries, Inc. 3,286,077 11/ 1966 Radford et a1. 156/583 X Hyaunis,Mm. 3,348,474 10/1967 Virta et al 156/583 X 3,408,476 10/1967 Wahl219/243 X 3,444,732 5/1969 Robbins et a1. 156/378 X [54] TEMPERATUREGRADIENT BAR SEALER 9 chin", 9 Drawing Primary Examiner-C. L. AlbnttonAttorney-Kenyon & Kenyon Reilly Carr and Chapm [52] US. Cl. 219/243,

100/93 P, 156/583 [51] Int. Cl. 1105b l/00 ABSTRACT: Apparatus for and aprocess of heat-sealing vari- [50] Field of Search... 219/243; ousmaterials such as plastics, papers, laminates and coatings.

156/378, 583; 73/ 15, 15 D; 100/93 1 The apparatus can be used forseveral purposes such as detera mining the optimum temperature at whicha given heat-sealing [56] Rflennm operation should be conducted undergiven conditions of UNITED STATES PATENTS pressure and dwell time and toeffect increased quality control 930,638 8/1909 Whitmore 219/255 x bymaintaining the temperature at the heat is Supplied 1,840,652 1/1932Bell 219 255, x during the heat-Sealing Operation under given conditionsof pressure and dwell time.

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AWE/7675 FIELD OF THE INVENTION This invention relates to the apparatusand method of heatsealing various materials which are widely used in thepackaging industry. The apparatus can be used as a laboratory testdevice to detennine what is the optimum temperature at which a givenmaterial should be heat-sealed. In the altemative the apparatus can beused as production line equipment to seal the packaging of various itemsand it enables a close control of the temperature being applied duringthe heat-sealing process.

DESCRIPTION OF THE PRIOR ART In prior art heat-sealing devices, thetemperature of the sealing bar has been controlled by sensing thetemperature at one location along the length of the bar. As a result thetemperature at other locations along the sealing bar can vary from thatof the controlled location.

In prior art gradient bar sealers, special electrical heating windingshave been employed to obtain a predetermined temperature gradient. Forexample the interval between adjacent turns of an electrical heatingwinding is varied in a cut-and-try manner and the winding is theninserted in a hole extending through the length of the sealing bar. Suchan arrangement is very difficult to construct, can only be done on acut-and-try basis to obtain a desired temperature gradient, and onceassembled cannot be varied or otherwise compensated.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a convenient, portable, inexpensive apparatus which can producevarious temperatures along the length of a bar used for heat sealing inorder that a technician by means of a single test can heat-sealmaterials over a range of temperatures. With one or more of such teststhe best temperature at which the given material should be heat-sealedcan be readily determined by examining the nature of the seal at variouspoints which correspond to a number of different sealing temperatures.It is another object of this invention to provide close control over thetemperature maintained along the length of a heatsealing bar by enablingthe temperature of the bar to be controlled in order that apredetermined temperature is produced at each point along the length ofthe heat-sealing bar. In this way a controlled amount of heat is appliedto the material which is being heat-sealed.

In one embodiment of the invention there is provided a machine forheat-sealing layers of material. A sealing bar applies heat along aportion of the material which has been placed beneath the sealing bar.The heat provided to each different portion of the bar is separatelycontrolled in order to obtain a number of different selectedtemperatures. In this way, one operation of the sealing bar enables anumber of dif ferent sealing temperatures to be evaluated at a selectedsealing pressure and dwell time.

The machine includes two elongated bars to form a jaw which grips thelayers of material. The temperature of the upper movable bar can be heldat a constant selected level along the entire length of the bar or thetemperature can be varied along the length of the bar from a lowtemperature such as 100 F. at one end of the bar to a high temperaturesuch as 550 F. at the opposite end of the bar.

A plurality of heating elements are embedded in the heating bar andspaced at substantially equal distances along the bar. These heatingelements produce a plurality of different temperature zones along thebar. The heating elements and their corresponding temperature zones canbe individually set by separate control mechanisms for differenttemperatures or for the same temperature.

Other objects and purposes of this invention will become obvious fromthe following disclosure.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational viewof the apparatus of the invention.

FIG. 2 is a vertical section view along the line 2-2 of FIG. I andshowing the sealing bar and its actuator.

FIG. 3 is a horizontal sectional view along the line 3-3 of FIG. 1 andshowing the plurality of controlled heating elements.

FIG. 4 is an enlarged fragmentary vertical section view of a portion ofFIG. 2 showing the material to be heat-sealed inserted between the jawsof the apparatus before the jaws of the apparatus are closed upon thematerial.

FIG. 5 is also an enlarged fragmentary vertical section view of aportion of FIG. 2 showing the material to be sealed inserted between thejaws of the apparatus with the jaws closed upon the material. 1

FIG. 6 is a perspective view of the edge portion of two sheets oftypical materials before they have been heat-sealed, that is, beforethey have been inserted between the jaws of the apparatus.

FIG. 7 shows the same sheets of material as shown in FIG. 6 after theedge portions of the sheets of the material have been heat-sealed, thatis, afier they have been removed from the jaws of the apparatus.

FIG. 8 is a graph depicting the temperature gradient along the sealingbar.

FIG. 9 is an electrical schematic diagram of the apparatus shown in FIG.I.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a front elevation viewof apparatus 10 of the invention. The apparatus includes upper and lowerjaws I1 and 12, respectively. The upper jaw and/or the lower jaw isheated by a plurality of electrical heater elements 13 which aredisposed in holes 14 positioned across the jaw and parallel to soleplate 15 (FIGS. 4 and 5). In operation heat flows from each of theheater elements through jaw 11 and into sole plate IS in order to raisethe sole plate to a temperature which is sufficient to heat-sealmaterial clamped between the jaws. Lower jaw I2 is provided with surfaceplate 16 (FIGS. 1, 4 and 5) upon which the material, such as sheets 17of thermoplastic material, are disposed prior to the closing of thejaws.

Upper jaw 11 is lowered from the elevated position shown in FIG. 4 tothe operative position shown in FIG. 5 by means of a plurality of fluidactuators 18 (FIGS. 1 and 2). Piston rods 18a of each of the actuatorsare coupled by plates 18b to the upper surface of jaw 11. The provisionof a plurality of actuators spaced at equal intervals along the entirelength of upper jaw 11 enables the upper jaw to apply a substantiallyuniformly distributed force or pressure to the work material disposedupon the lower jaw. The number of actuators is determined by the lengthof the upper jaw. By way of example when the upper jaw is approximately24 inches long, four actuators 18 such as shown in FIG. 1 are sufficientfor applying the necessary sealing force. Upper jaw 11 is returned fromits operative position to its elevated position by means of tensionsprings (not shown) extending from the upper jaw to a frame member ofthe apparatus. Thus whenever fluid pressure is released from theactuators the springs raise the upper jaw.

As shown in FIG. 2 each of the actuators 18 is connected to manifold 19.When the upper jaw 11 is to be lowered, solenoid valve 20 is actuated toconnect a flow of fluid at regulated pressure from pressure regulator 21to line 22 leading to manifold 19. The regulated pressure is connectedby line 23 to gauge 24 (FIGS. 1 and 2) which can be calibrated toindicate the pressure applied by the jaws to the material being sealed.Thus the regulated pressure is converted to sealing pressure by means ofthe scale on gauge 24. By means of knob 21a the operator of the machinecan set the level of the regulated pressure to be applied to theactuators of the upper jaw and thereby set a predetermined jaw pressurewhich for example can be in the range of 5 p.s.i. to p.s.i.

Whenever solenoid valve 20 is connecting the controlled pressure fromregulator 21 to line 22 and thereby the inanifold, the controlledpressure causes dump valve 56 toclose. When valve 20 closes, thepressure in line 22 is reduced. Valve 56 opens when the pressure in line22 is reduced and the dump valve 56 then connects line 56a and therebythe manifold to the atmosphere through exhaust port 56b. The purpose ofthe dump valve is to speed the evacuation of pressured fluid from theactuators whenever solenoid valve 20 is closed so that the tensionsprings can immediately raise the upper jaw to its elevated position.But for the dump valve it would be necessary for the tension springs toovercome the fluid pressure resulting from the need to evacuate theactuators through line 22 and solenoid valve 20.

As shown in FIGS. 4 and the upper jaw 11 is provided with a thermocouple26 inserted in well 27 adjacent to heater element 13. Thus eachthermocouple is exposed to the temperature of the sole plate adjacenteach of the heating elements. Each of thermocouples 26 are connected toa different one of a plurality of pyrometers 28 which are calibratedmicrovolt meters (FIGS. 1 and 2). As a result the temperature conditionsat various locations along the sole plate are directly indicated by thepyrometers.

Power is supplied to the heater elements by line 29 F IG. 9) which isconnected through switch 30 to power source 31. Each of heater elements13 is connected to the wiper of a different one of a plurality ofvariable transformers 33. In turn the winding of the transformer isconnected across lines 29 and 32. Line 32 is connected by line 34 totemperature controller 35 which is adapted to energize line 34. It canbe seen that by adjusting the variable transformers 33 whenever thetemperature controller energizes line 34 and thereby the transformers,it is possible to set a predetermined temperature condition for eachportion of the sole plate of the upper jaw.

Temperature controller 35 is adapted to control the temperature ofelectrical heater element 36 which is similar in construction to that ofelements 13 and is mounted in a hole similar to hole 14 in the upperjaw. By way of example element 36 can be disposed at one end of theupper jaw as shown in FIG. 3. Thermocouple 37 is mounted adjacent toheater element 36 in a manner similar to that of the mounting ofthermocouples 26. The temperature control (FIG. 1) which can be ofconventional construction is adapted to energize line 34 whenever thetemperature set by means of dial 38 is different from the actualtemperature at thermocouple 37. Thermometer 39 indicates the actualtemperature in response to the thermocouple. Thus whenever thetemperature of the sole plate of the upper jaw is below the requiredtemperature set at dial 38, controller 35 energizes line 34 and therebyheater element 36. At the same time the energizing of line 34 energizesall of variable transformers 33 which in turn energize their respectiveheater elements 13.

In accordance with the calibration procedure the operator initiallyselects the reference temperature to be maintained at the location ofthermocouple 37 by setting dial 38. By means of variable transformers 33the operator can then adjust the temperature sensed at each ofthermocouples 26 to be in a predetermined relationship with thetemperature being maintained by the controller. For example thetemperature of the sole plate adjacent to element 36 (FIG. 3) can bethat corresponding to number 1 on the graph 40 of FIG. 8. Thetemperatures adjacent the remaining elements 13 are those correspondingto numbers 2-8 of the graph. Thus in accordance with the example it canbe seen that each of the heater elements 13 can be adjusted intemperature to be elevated with respect to the temperature of heaterelement 36 in the manner of a straight line as shown by the graph. Withsuch an arrangement it can be seen that a predetermined temperaturegradient can be set for the length of the sole plate of the upper jaw.With such a gradient it can be understood that upon forming a heat seal,the sealing temperature at each point of the seal would correspond to adifferent temperature as shown by the graph. Consequently the forming ofa single seal provides test results of a range of sealing temperatures.In effect one test cycle gives the results as far as variable sealingtemperatures are concerned of the equivalent of an appreciable number oftest cycles. Thus the test procedure is greatly simplified as far as thetemperature variable is concerned and the operator is enabled to thenconcentrate the test investigation as to the sealing pressure and dwelltime variables.

It should be noted that the temperature characteristic of the heaterelements can be varied in other predetermined manners with respect tothe temperature adjacent element 36. Thus the characteristic need not bean increase in tempera-' ture. Instead a uniform temperature could bemaintained along the bar. In addition elements 13 can be controlled toheat the sole plate at temperatures extending below that of element 36.Furthermore elements 13 could be maintained at temperatures both aboveand below element 36. With the advantage'of being capable of maintaininga wide range of tem-v perature characteristics along the sealing bar itcan be understood that the apparatus and method of the invention can beused both for laboratory as well as production purposes.

In order to control the dwell time of the application of the sealingforce to the material the apparatus of the invention is provided withtimer 41 which is of a conventional construction. The timer includestiming motor 42 which operates switches 43 and 44. In order to place theapparatus in operation, the operator initially closes main powerswitches 31. The operator then sets temperature controller 35 at therequired reference temperature. It is then necessary for the operator toadjust variable transformers 33 in order that a predeterminedtemperature characteristic or gradient be indicated by pyrometers 28 Bymeans of knob 46, the operator sets the dwell time of the application ofsealing pressure to the workpiece. Knob 46 is coupled in a conventionalmanner to timer 41.

When the temperature of the sealing bar of upper jaw 11 has stabilizedand the pyrometers indicate that the desired temperature condition ispresent along the sealing bar, the operator places the material to besealed between the jaws II and 12. Foot switch 45 is then depressed bythe operator. The foot switch completes a circuit to relay 47 throughswitch 44 which is in its normally closed position. The energization ofrelay 47 closes contacts 47a which furnish a holding circuit for therelay. At the same time solenoid winding 20a of solenoid valve 20 isenergized and causes fluid pressure to be applied to actuators 18. Inthis way the sole plate of the upper jaw'is lowered into engagement withthe workpiece.

The descent of the upper jaw engages and closes limit switch 48. Thelimit switch 48 is positioned with respect to the upper jaw so that theswitch can only be closed when the upper jaw has descended intoengagement with the material to be sealed. The closing of switch 48energizes timing motor 42 and begins the timed cycle. At the conclusionof the time period set by knob 46 of timer 41, the timer causes switch44 to be opened with respect to relay 47 which thereby deenergizes therelay.

The deenergizing of the relay results in the opening of relay contacts47a which previously had provided the holding current to relay 47following the release of the foot-operated switch 45. The opening ofswitch 44 also causes solenoid winding 20a to be deenergized and, as aresult, solenoid valve 20 opens and causes dump valve 56 to void theactuators. Consequently the dump valve evacuates fluid pressure fromactuators l8 and permits the tension springs to elevate the upper jaw.

When timing motor 42 opens switch 43, the time cycle has been completed;however the timing motor continues to run in response to the closedlimit switch 48 until the timing motor recycles switches 43 and 44 andprepares the system for the next actuation of foot-switch 45. Limitswitch 48 opens as soon as the actuators 18 are voided and the tensionsprings elevate the upper jaw.

When the nature of the material being sealed should warrant it, lowerjaw 12 may be provided with passages through which a coolant such aswater can be directed. In this way the Apparatus for heat-sealingmaterial comprising:

a bar having a surface extending along its length adapted to apply heatto material to be heat-sealed, said bar being formed of heat-conductivematerial extending continuously from one end to the other thereof andproviding thereby a continuous thermal conductive path from one end tothe other;

a plurality of sources of heat mounted upon said bar spaced apart fromone another along the length of said bar; means for controlling each ofsaid plurality of sources of heat to maintain a predetenninedtemperature at the surface of said bar adjacent to each of saidplurality of sources of heat; an additional source of heat mounted onsaid bar; and means responsive to the relation of the temperature at thesurface of said bar adjacent to said additional source to a preselectedtemperature for activating said additional source of heat to maintainsaid preselected temperature and for actuating said plurality of sourcesof heat concurrently therewith while said plurality of heat sourcesremain subject to said controlling means, whereby a predetermined andcontinuously varying temperature condition, extending lengthwise alongthe surface of said bar, can be maintained.

. A machine for heat-sealing material comprising: a pair of jawsincluding two bars formed of heat-conductive material extendingcontinuously from one end of each bar to the other and providing therebya continuous thermal conductive path from one end of each bar to theother, one bar being a stationary bar and the other bar being a movablebar, the bars being disposed in a horizontal position parallel to oneanother, the movable bar being positioned above the stationary bar inorder that material to be sealed can be disposed between said pair ofjaws and that said jaws when closed can apply sealing pressure to thematerial to be heat-sealed;

a plurality of electrical heating elements disposed on at least one ofsaid bars along the length thereof;

means for varying the circuit resistance of said heating elements, eachof said heating elements producing a temperature zone adjacent itself;

. a different variable transformer connected to each of said heatingelements to vary the temperature of each of said heating elements;

. a different temperature indicator for each of the zones means forpredetermining the dwell time during which the jaws are closed and thematerial is being heat-sealed;

an additional source of heat mounted on said bar; and means responsiveto the relation of the temperature at the surface of said bar adjacentto said additional source to a preselected temperature for activatingsaid additional source of heat to maintain said preselected temperatureand for actuating said plurality of sources of heat concurrentlytherewith while said plurality of heat sources remain subject to saidcontrolling means.

A method for heat-sealing a material by means of a bar having apredetermined temperature characteristic, the bar being formedof'heat-conductive material extending continuously from one end to theother end thereof and providing thereby a thermal conductive path fromone end of the bar to the other, said bar having along its length asurface adapted to apply heat to material to be heat-sealed, and aplurality of sources of heat being spaced apart from one another alongthe length of said bar, comprising the steps of:

maintain a predetermined temperature at said surface of the bar adjacentto each source of heat;

b. applying the surface of the bar to the material to be heatsealed;

c. providing an additional source of heat on the bar; and

d. actuating the additional source of heat to maintain a preselectedtemperature at the surface of said bar ad jacent to the additionalsource and actuating said plurality of sources of heat concurrentlytherewith while the plurality of heat sources remain subject to the stepof controlling, whereby a predetermined temperature condition extendingand varying continuously along said surface of the bar can bemaintained.

4. Apparatus for heat-sealing material comprising:

a. a bar having a surface extending along its length adapted to applyheat to material to be heat-sealed, said bar being formed ofheat-conductive material extending continuously from one end to theother thereof and providing thereby a continuous thermal conductive pathfrom one end to the other;

b. a plurality of sources of heat mounted upon said bar spaced apartfrom one another along the length of said bar;

heat to maintain a predetermined temperature at the surface of said baradjacent to each of said plurality of sources of heat; means mounted onsaid bar adjacent each of said plurality of sources of heat forproducing an electrical signal which is a function of the temperature ofthe surface of the bar adjacent each of said plurality of sources ofheat; and e. a plurality of means connected to each of said plurality ofsignal producing means for simultaneously indicating each temperature ofwhich each of the electrical signals of said signal producing means is afunction, whereby a predetermined and continuously varying temperaturecondition, extending lengthwise along the surface of said bar, can bemaintained. 5. Apparatus in accordance with claim 1 and furthercomprising:

a. an additional bar disposed spaced apart with its length substantiallyparallel to that of said bar; and b. means for moving at least one ofsaid bar and said additional bar relative to one another in the mannerof a pair of jaws between an opened position and a closed position undercontrolled closing force, said moving means enabling said bar andadditional bar to apply a controlled sealing pressure to materialdisposed therebetween.

6. Apparatus in accordance with claim 5 in which said means for movingat least one of said bar and said additional bar relative to one anotherin the manner of a pair of jaws comprises a plurality of actuatorsdisposed along the length of at least one of said bar and saidadditional bar for applying a uniformly distributed force to produce auniformly distributed sealing pressure.

7. Apparatus in accordance with claim 6 in which said plurality ofactuators are operated in response to the application of fluid pressurethereto and further comprising means for controlling the magnitude offluid pressure to be applied to said plurality of actuators, whereby thesealing pressure is determined.

8. Apparatus in accordance with claim 5 and further comprising means formaintaining said means for moving at least one of said bar and saidadditional bar relative to one another in the closed position for apredetermined period of time, whereby the dwell time period of theapplication of sealing can be controlled.

9, Apparatus in accordance with claim 8 in which said means formaintaining said moving means in the closed posimeans for controllingeach of said plurality of sources of

1. Apparatus for heat-sealing material comprising: a. a bar having asurface extending along its length adapted to apply heat to material tobe heat-sealed, said bar being formed of heat-conductive materialextending continuously from one end to the other thereof and providingthereby a continuous thermal conductive path from one end to the other;b. a plurality of sources of heat mounted upon said bar spaced apartfrom one another along the length of said bar; c. means for controllingeach of said plurality of sources of heat to maintain a predeterminedtemperature at the surface of said bar adjacent to each of saidplurality of sources of heat; d. an additional source of heat mounted onsaid bar; and e. means responsive to the relation of the temperature atthe surface of said bar adjacent to said additional source to apreselected temperature for activating said additional source of heat tomaintain said preselected temperature and for actuating said pluralityof sources of heat concurrently therewith while said plurality of heatsources remain subject to said controlling means, whereby apredetermined and continuously varying temperature condition, extendinglengthwise along the surface of said bar, can be maintained.
 2. Amachine for heat-sealing material comprising: a. a pair of jawsincluding two bars formed of heat-conductive material extendingcontinuously from one end of each bar to the other and providing therebya continuous thermal conductive path from one end of each bar to theother, one bar being a stationary bar and the other bar being a movablebar, the bars being disposed in a horizontal position parallel to oneanother, the movable bar being positioned above the stationary bar inorder that material to be sealed can be disposed between said pair ofjaws and that said jaws when closed can apply sealing pressure to thematerial to be heat-sealed; b. a plurality of electrical heatingelements disposed on at least one of said bars along the length thereof;c. means for varying the circuit resistance of said heating elements,each of said heating elements producing a teMperature zone adjacentitself; d. a different variable transformer connected to each of saidheating elements to vary the temperature of each of said heatingelements; e. a different temperature indicator for each of the zonesalong the length of the bar to indicate the temperature of each suchzone, at least a portion of each of said indicators being in thermalcommunication, respectively, with each related temperature zone; f.means for predetermining the jaw pressure to be applied to the materialto be heat-sealed; g. means for predetermining the dwell time duringwhich the jaws are closed and the material is being heat-sealed; h. anadditional source of heat mounted on said bar; and i. means responsiveto the relation of the temperature at the surface of said bar adjacentto said additional source to a preselected temperature for activatingsaid additional source of heat to maintain said preselected temperatureand for actuating said plurality of sources of heat concurrentlytherewith while said plurality of heat sources remain subject to saidcontrolling means.
 3. A method for heat-sealing a material by means of abar having a predetermined temperature characteristic, the bar beingformed of heat-conductive material extending continuously from one endto the other end thereof and providing thereby a thermal conductive pathfrom one end of the bar to the other, said bar having along its length asurface adapted to apply heat to material to be heat-sealed, and aplurality of sources of heat being spaced apart from one another alongthe length of said bar, comprising the steps of: a. controlling each ofsaid plurality of sources of heat to maintain a predeterminedtemperature at said surface of the bar adjacent to each source of heat;b. applying the surface of the bar to the material to be heat-sealed; c.providing an additional source of heat on the bar; and d. actuating theadditional source of heat to maintain a preselected temperature at thesurface of said bar adjacent to the additional source and actuating saidplurality of sources of heat concurrently therewith while the pluralityof heat sources remain subject to the step of controlling, whereby apredetermined temperature condition extending and varying continuouslyalong said surface of the bar can be maintained.
 4. Apparatus forheat-sealing material comprising: a. a bar having a surface extendingalong its length adapted to apply heat to material to be heat-sealed,said bar being formed of heat-conductive material extending continuouslyfrom one end to the other thereof and providing thereby a continuousthermal conductive path from one end to the other; b. a plurality ofsources of heat mounted upon said bar spaced apart from one anotheralong the length of said bar; c. means for controlling each of saidplurality of sources of heat to maintain a predetermined temperature atthe surface of said bar adjacent to each of said plurality of sources ofheat; d. means mounted on said bar adjacent each of said plurality ofsources of heat for producing an electrical signal which is a functionof the temperature of the surface of the bar adjacent each of saidplurality of sources of heat; and e. a plurality of means connected toeach of said plurality of signal producing means for simultaneouslyindicating each temperature of which each of the electrical signals ofsaid signal producing means is a function, whereby a predetermined andcontinuously varying temperature condition, extending lengthwise alongthe surface of said bar, can be maintained.
 5. Apparatus in accordancewith claim 1 and further comprising: a. an additional bar disposedspaced apart with its length substantially parallel to that of said bar;and b. means for moving at least one of said bar and said additional barrelative to one another in the manner of a pair of jaws between anopened position and a closed position under controlled closing force,said moVing means enabling said bar and additional bar to apply acontrolled sealing pressure to material disposed therebetween. 6.Apparatus in accordance with claim 5 in which said means for moving atleast one of said bar and said additional bar relative to one another inthe manner of a pair of jaws comprises a plurality of actuators disposedalong the length of at least one of said bar and said additional bar forapplying a uniformly distributed force to produce a uniformlydistributed sealing pressure.
 7. Apparatus in accordance with claim 6 inwhich said plurality of actuators are operated in response to theapplication of fluid pressure thereto and further comprising means forcontrolling the magnitude of fluid pressure to be applied to saidplurality of actuators, whereby the sealing pressure is determined. 8.Apparatus in accordance with claim 5 and further comprising means formaintaining said means for moving at least one of said bar and saidadditional bar relative to one another in the closed position for apredetermined period of time, whereby the dwell time period of theapplication of sealing can be controlled. 9, Apparatus in accordancewith claim 8 in which said means for maintaining said moving means inthe closed position for a predetermined period of time is activated inresponse to the closing of said bar with respect to said additional bar.